In recent years, bolts called Torshear Bolts (hereinafter referred to as “shear bolts”) have been used for screw-fastening in steel-frame buildings, where they are screw-fastened by nuts. Screw-fastening by a nut is performed in a two-stage double fastening, i.e., primary fastening and final fastening. A nut-fastening tool, which is disclosed in Japanese Patent Publication No. 2009-297858, has been used for fastening such a type of nut. The above-described nut-fastening tool can be turned on by pulling an operation trigger that is provided in a tool main body.